In one known control device of this type, two semi-circular members are mounted for angular movement about respective mutually orthogonal axes extending diametrically across the ends thereof. Each semi-circular member has a slot extending along the length thereof and a control lever projects through the slot of the two semi-circular members and is pivotally mounted at the point of intersection of the said orthogonal axes. A respective potentiometer is coupled to each of the semi-circular members. This device is subject to an undesirable amount of backlash, due to the flexibility of the semi-circular members, particularly when the control lever is in the quadrant of the control device opposite to the quadrant bounded by the two potentiometers. In another known control device, this problem is overcome by mounting one of the potentiometers within the semi-circular members. However it is then impossible to provide for a trim adjustment to be made between the angular position of each potentiometer and its corresponding semi-circular member. With such a control device it is usually necessary to provide electrical trimming arrangements in the circuits connected to the potentiometers which are thereby unnecessarily complicated.